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Structural, pressure-dependent resistivity, angle resolved photoemission spectroscopy (ARPES), x-ray photoelectron diffraction (XPD) and band structure by DFT calculation have been investigated for BiSbTe3 Topological insulator. It has been demonstrated that the Dirac point of the topological surface state (TSS) located exactly at the Fermi level. Additionally, superconductivity emerges under pressure of 8 GPa with a critical temperature of ∼2.5 K. With further increase of pressure, the superconducting transition temperature (Tc) increases and at 14 GPa it shows the maximum Tc (∼3.3 K). It has also been shown that the surface state remains unchanged under pressure and has been suggested that the origin of the superconductivity is due to the bulk state. The investigation indicates that the BiSbTe3 has robust surface states and becomes superconductor under pressure.

Magnetic topological semimetals (TSMs) with broken time-reversal symmetry are very rare and have drawn significant attention in condensed matter physics due to their numerous intriguing topological properties. Among these various magnetic TSMs, Co$_2$-based full Heusler compounds are of current interest, since a few of these materials exhibit Weyl and nodal fermions in their topological band structure. In this work, we report a comprehensive study of anomalous Hall effect (AHE) in the ferromagnetic full Heusler compound Co$_2$VAl. Recent studies indicate that the intrinsic AHE is closely related to the Berry curvature of the occupied electronic Bloch states. The present study of Co$_2$VAl attempts to understand and explore the possibility of topology-induced AHE. The anomalous Hall resistivity $\rho^A_{xy}$ is observed to scale quadratically with the longitudinal resistivity $\rho_{xx}$. Our experimental results also reveal that the anomalous Hall conductivity (AHC) is $\sim 85\, S/cm$ at 2 K with an intrinsic contribution of $\sim 75.6\, S/cm$, and is nearly insensitive to temperature. The first principle calculations note that the Berry curvature originated from a gapped nodal line and symmetry-protected Weyl nodes near the Fermi level ($E_F$) is the main source of AHE in this compound. Thus, this investigation on Co$_2$VAl discloses that it is a ferromagnetic Weyl and nodal-line topological semimetal. The theoretically calculated AHC is in well agreement with the experimentally obtained AHC.

Ferromagnetic (FM) semimetals FenGeTe2(n=3, 4, 5), exhibit several symmetry-protected bandcrossing points or lines near the Fermi energy (EF ) and these topological properties of energy bands lead to interesting transport properties. We study these materials employing the first-principle calculations and the tight-binding Hamiltonian constructed by fitting the parameters of the first principles calculation. In the presence of spin-orbit coupling (SOC) for n=3,5 a large Berry curvature (BC) concentrated on the nodal lines is observed. The consequence of the correlation of the topological nodal line and magnetic moments on anomalous Hall conductivity (AHC) σxy and anomalous Nernst conductivity (ANC) αxy have been investigated. We find σxy = 150 S/cm for n=3, 295 S/cm for n=4, and 90 S/cm for n=5 at 0 K, while the ANC is observed as αxy = 0.55 A/Km for n=3, 0.10 A/Km for n=5, and 0.80 A/Km for n=4, at the EF at room temperature. Our calculated AHC values at 0 K, i.e., 150 S/cm for Fe3GeTe2 and 90 S/cm Fe5GeTe2, are consistent with the experimentally reported values. Also the experimentally reported value of ANC for Fe5GeTe2 is close to our calculated value at room temperature, i.e., 0.10 A/Km.

The anomalous transport properties of Heusler compounds become a hotspot of research in recent years due to their unique band structure and possible application in spintronics. In this paper, we report the anomalous Hall effect in polycrystalline NiCoMnGa quaternary Heusler compound by experimental means and theoretical calculations. The experimental anomalous Hall conductivity (AHC) was found at about 256 S/cm at 10K with an intrinsic contribution of ∼ 121 S/cm. The analysis of Hall data reveals the presence of both extrinsic and intrinsic contributions in AHE. Our theoretical calculations show that a pair of spin-orbit coupled band formed by the band splitting due to spin-orbit interaction (SOI) at the Fermi level produces a finite Berry flux in the system that provides the intrinsic AHC about 100 S/cm, which is in good agreement with the experiment.